def add(x,lst=None):
    if lst ==None:
        lst = []

    if x not in lst:
        lst.append(x)
    return lst

def main():
    list1 = add(1)
    print(list1)

    list2 = add(2)
    print(list2)

    list3 = add(3,[1,2,3,4,5])
    print(list3)

    list4 = add(4)
    print(list4)

main()